BAGRAM, Afghanistan - U.S. and Afghan forces battled rebels aligned with renegade leader Gulbuddin Hekmatyar on Tuesday in the largest-scale fighting in Afghanistan in 10 months.

At least 18 rebels were killed in the fighting, which began Monday in the southeastern mountains, the U.S. military said. There were no Afghan coalition casualties or civilian injuries.

The military said 80 rebels were involved in the conflict, and - on the American side - up to 350 soldiers, including troops from the 82nd Airborne division, U.S. Special Forces, and allied Afghan militia troops.

"It's the largest concentration of enemy forces since Operation Anaconda," U.S. military spokesman Roger King said from Bagram Air Base, referring to a fierce eight-day battle last March against Taliban and al-Qaida holdouts in southeastern Afghanistan.

Fighters received aerial support from American B-1 bombers dropping 19 2,000-pound bombs on enemy positions, including deep caves, King said. F-16 fighters flown by European allies dropped a pair of 500-pound bombs, while AC-130 gunships and Apache AH-64 helicopter gunships pounded the enemy with rocket and cannon fire, King said.

"We've had reports of various numbers of armed men, groups of people trying to gather in order to carry out attacks on the coalition," King said. "We've been actively engaged in trying to develop intelligence that would lead us to a precise location and yesterday we did."

The fighting - about 15 miles north of Spinboldak and near the border with Pakistan - was triggered by a small shootout pitting armed attackers against U.S. Special Forces and their Afghan government allies working to clear a mud-walled compound.

One attacker was killed, one injured and one detained, King said. The detained suspect told questioners that a large group of armed men had massed in mountains nearby.

Apache helicopters sent to investigate came under small arms fire, and then fighter aircraft went to pound the area.

"Our intelligence leads us to believe that they are most closely aligned with the Hezb-e-Islami movement, which is Hekmatyar's military arm," King said. "We've had reports over several months that he's been attempting to consolidate with remnants of al-Qaida and Taliban."

Hekmatyar was a key guerrilla commander during the 1980s Soviet war in Afghanistan. Later, in the civil war that paved the way for the Taliban takeover, Hekmatyar's men pounded the capital, Kabul, with daily rocket barrages. He lived in exile in Iran during the five years of Taliban rule, and returned after U.S.-led forces ousted the hardline militia. Western intelligence agencies suspect he is getting money from Iran.

His following among ethnic Pashtuns is considered fairly significant.

Reports that Hekmatyar was training suicide squads to target American and government forces surfaced in September, when one of Hekmatyar's military commanders, Salauddin Safi, told The Associated Press that some Taliban had formed an alliance with Hekmatyar's followers called Lashkar Fedayan-e-Islami, or the Islamic Martyrs Brigade.

King would not speculate on what the guerrillas were planning, but said the largest contingent of coalition forces was stationed in nearby Spinboldak. "That's an obvious target," he said.

King said the latest battle might last some time.

"It's a relatively large area ... There are some caves, there may be more that we don't know about, so it could take a considerable period of time," King said. He said fighting was centered on rocky and rough terrain in an unpopulated around the Adi Ghar mountain.

King said it is believed the rebel fighters, while loyal to Hekmatyar, may have links to the ousted Taliban and al-Qaida. Because the fighting was near the border, it was possible that fighters of other nationalities were involved, he said.

Many Taliban and al-Qaida suspects fled into Pakistan following U.S. bombardment in late 2001. U.N. and American forces have expressed concern about renewed training by al-Qaida and Taliban militants in southeastern Aghan mountains, near the border.

There have been a series of attacks along the border in recent months, including one in December that left one U.S. army sergeant dead. Rockets frequently are fired at U.S. bases in that region but rarely hit their targets.

King wouldn't say whether U.S. troops might pursue rebels into Pakistan if they fled over the border.

"I have no indication that it would come to that. Entry into Pakistan should not come up with this action," King said. Pakistan has said U.S. troops won't be permitted to pursue the enemy into Pakistan.